Simultaneous interactions of anions and cations with cyclohexane and adamantane: Aliphatic cyclic hydrocarbons as charge insulators

With ab initio MP2 computational methods, a theoretical study has been carried out to characterize the interaction between aliphatic cyclic hydrocarbons, as models of molecular hydrocarbon monolayers, with cations (Li ⁺, Na ⁺, and K ⁺), anions (F ^-, Cl ^-, and Br ^-), and both simultaneously in opposite faces of the hydrocarbons. In addition, the energetic barrier for the cation crossing through the hydrocarbon ring has been calculated. The hydrocarbons chosen for this study are cyclohexane (C ₆H ₁₂) and adamantane (C ₁₀H ₁₆). The energies obtained for the M ⁺:hydrocarbon:X ^- complexes indicate positive cooperativity in the cases where the hydrocarbon is cyclohexane while diminutive effects are found in the adamantane complexes. The density functional theory-symmetry adapted perturbation theory analysis of the interaction energies shows that the most important term in the complexes with cations is the induction, while in the complexes with anion and with cations and anions simultaneously the most important term is the repulsion-exchange one. The electron density of the complexes has been analyzed using the atoms in molecules methodology and provides some insight to the electron transfer within the complexes.